The proposed research will evaluate the mechanisms by which hormones regulate the growth of kidney epithelial cells, and the alterations which occur upon malignant transformation. Medium K-1, and available hormone-supplemented, serum-free medium for a kidney epithelial cell line, MDCK, will be utilized for the following studies: a) The mechanism by which PGE1 (a hormone in Medium K-1) stimulates MDCK cell growth will be examined. Available PGE1 independent variants of MDCK cells (variants which lack the PGE1 requirement for long term growth in serum-free medium) will be utilized. b) the possibility that malignant transformation is accompanied by changes in the requirements of hormones for growth will be evaluated, utilizing available tumorigenic transformants of MDC cells. c) Growth regulation by hormones will also be examined in primary culures of kidney epithelial cells. Medium K-1 was utilized to select epithelial cells from primary kidney cultures, whose growth responses to hormones resemble those of MDCK cell. In order to selectively grow different types of epithelial cells in primary kidney cultures, additional hormone-supplemented, serum-free media will be developed for kidney epithelial cell lines which do not grow in Medium K-1.